Generally, in an image forming apparatus of an electro-photographic printing system such as a copying machine, a printer, a facsimile machine, etc., toner as sequentially supplied onto the surface of a developer roller of a developing device is carried onto the surface of the developing roller of the developing device by rotating the developer roller to develop (visualize) an electrostatic latent image on the surface of the photoreceptor.
In the case of the developing device for developing non-magnetic toner of one-component, toner particles are sequentially supplied in a circumferential direction onto the surface of the developing roller by means of a supply roller, and further the toner particles held on the developer roller are carried by rotating the developing roller. Then, the thickness of the toner layer is regulated by a blade provided at the downstream side of the supply roller in the rotation direction of the developer roller. In the meantime, the toner is charged by friction with the blade (friction charge). The toner as charged is carried onto the part facing the photoreceptor provided on the downstream side in the rotation direction, and is further supplied electro-statically to an electro-static latent image formed on the surface of the photoreceptor, thereby developing (visualizing) the electrostatic latent image to be a toner image. After being transferred onto the recording sheet, with an application of the heat and pressure, the toner image as visualized is affixed onto the recording sheet as a permanent image.
In the foregoing conventional technique of charging the toner by the friction with the blade, the blade is pressurized onto the developing roller with large application force, to regulate the thickness of the toner layer and charge the toner at the same time.
In the foregoing method of utilizing the friction charge, it is liable that a heavy load is incurred onto the toner, or toner is damaged, or softened to be melted on the surface of the blade, which results in deterioration of friction charge characteristics between the blade surface and the toner.
Namely, according to the foregoing conventional techniques, the developing agent is rubbed to charge the developing agent, which causes such problem that the developing agent is damaged by friction, or the damaged developing agent adhering to a recording material, etc., resulting in lower image quality.